In the manufacturing of semiconductor wafers, manufacturing equipment include many apparatuses for performing the various processes. Each of the apparatuses has a corresponding operation environment, e.g. oxygen-rich, oxygen-poor, oxygen-free, and high vacuum environments. If there is deviation of the operation environment, undesired defect would form accordingly. For example, in a thin film process, particles caused by unexpected oxidation may substantially damage the yield of semiconductor wafers. Therefore, a well controlled working environment is needed to ensure delivery of high quality products on a consistent basis.
Working environment control is challenging to a modern semiconductor fabrication facility because the ball room becomes larger for accommodating more equipments than before. To save the cost, the ball room is typically maintained at a constant temperature and humidity, but possibly not appropriate to semiconductor wafers at certain stages. Thus, semiconductor wafers are usually kept in a pod with mini-environment during transportation or in queue to prevent any cross contamination. However, it is unavoidable that semiconductor wafers are exposed to the ambient environment or atmosphere during certain processes, especially during the transfer from an opened pod to a manufacturing equipment. Therefore, unexpected defect(s) might form on semiconductor wafers and their origins are often difficult to trace. Under some circumstances, semiconductor wafers left in an environment over a predetermined period of time, i.e., queue time (Q-time), will also increase the chance of unexpected defects.
In view of the foregoing, it is greatly desired to develop an apparatus or method to prevent defects in the semiconductor wafers particularly when the gas tight seal of the pod needs to be broken, or when the wafer(s) have remained in an environment over an extended period of time.
Like reference symbols in the various drawings indicate like elements.